Disease alert: soybean downy mildew

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Disease surveys across southern Queensland have revealed a high incidence of Downy mildew in several soybean crops in April 2022. The downy mildew pathogen, Peronospora manshurica, infects crops during periods of rainy, humid weather. Though widespread, the disease is likely to have a minimal impact on yields.

The pathogen can survive between soybean crops in infected seeds, on volunteer soybeans or alternative hosts, and in soil and stubble. Plants infected with downy mildew have small light green to yellow spots on the upper leaf surface. A grey or tan coloured fungal growth often develops from the spots on the lower leaf surface during wet and humid conditions.

Light green to yellow spots on upper leaf surface caused by the soybean downy mildew pathogen. Tufts of tan or grey fungal mycelium develops on the lower leaf surface on the underside of the spots. Photo: Lisa Kelly

Further information on downy mildew can be found at:

If you see disease symptoms in grain crops and require further information on diagnosis, please contact plant pathologist Lisa Kelly ([email protected], 0477 747 040).

This research is supported by the Grains Research and Development Corporation (GRDC) and co-invested by DAF through the project Disease surveillance and related diagnostics for the Australian grains industry (within the Northern region) (DAQ2106-007RTX).